Fiber reinforced polymer composites are well known and widely used. Polymers of improved strength and increased stiffness can be obtained by use of an appropriate reinforcing fiber. Probably the most widely used reinforcing fibers are glass, carbon and aramid.
The base polymers used in making polymer composites such as those described above include a wide range of thermoplastics, such as polystyrene and copolymers thereof, polyamides, polycarbonate, polyetheramide, polyetherketone (PEEK) and polyesters such as polybutylene terephthalate. These polymers may either be amorphus or semi-crystalline. They may be called flexible chain polymers, since individual monomer units in the polymer chain are free to rotate with respect to each other so that the polymer chain will assume a random shape. Numerous references, including by way of illustration, F. N. Cogswell, Intern. Polymer Processing, vol. 1, no. 4, pp 157-165 (1987) disclose such polymers.
U.S. Pat. No. 4,820,568 to Harpell et al discloses a multi-layer composite laminate comprising a plurality of prepreg layers, in which each layer comprises high strength preformed fibers of a conventional fiber reinforcing material, (e.g., carbon, graphite, cellulose or metal) in a flexible chain polymer matrix.
Self-reinforced polymer composites comprising microscopic liquid crystal (or wholly aromatic polyester) fibers formed in situ in a matrix of flexible chain thermoplastic polymer have been developed in recent years. U.S. Pat. Nos. 4,728,698 and 4,835,047 both to Isayev et al, illustrate such composites. The essentially unidirectionally oriented fibers are formed by application of high strain mixing conditions.
Also known are polymer blends of two or more melt processable wholly aromatic polyesters, each of which is capable of forming anisotropic melt phase (i.e., a liquid crystal polymer). Such blends are disclosed, for example, in U.S. Pat. Nos. 4,267,289 to Froix and 4,837,268 to Matsumoto et al. Both references disclose the formation of injection molded articles for new respective polymer blends, but neither discloses the formation of reinforcing fibers in situ, and both carry out injection molding at a temperature at which both (or all) polymers are melt processable.
U.S. Pat. No. 5,070,157 to Isayev et al, issued Dec. 3, 1991, discloses polymer blends of two wholly aromatic polyesters of liquid crystal polymers having different melting points or glass transition temperatures, so that one of these polymers is capable of forming fibers in situ in a matrix of the other, and further discloses injection molding of such blends, but at a temperature at which both or all liquid crystal polymers are melt processable.